It seems clear that with Pierce you may choose to cancel up to X block results. And with that choosing, you could in theory not use Pierce one time to keep one trooper alive in a unit so as to keep the attacker engaged in melee and therefore unable to be shot at range.
Can you just choose not to add Pierce to the attack pool to begin with? I am wondering how this choosing interacts with the Impervious keyword. Can you simply choose not to use Pierce to begin with and therefore not grant the extra dice from Impervious?
